Dave Wagner has already ably answered part of your query, but I thought
I would add a few comments.
Yes, you can stick to the FORTRAN subset of Mathematica, but it is
often easier to make at least limited use of the other features of
the language.
Reformulate your problem, as follows:
Let x be a list of real numbers. We need a list y that is the same
size as x, but where if element i of x is a then the corresponding
element of y should be Line[ { { 5, 25 }, { a, a^2 } } ].
Mathematically, this is a mapping. Then Show[ Graphics[ y ] ].
The following should do this:
x = { 5, 5.5, 5.4, 5.3 };
makeLine[ x_ ] := Line[ { { 5, 25 }, { x, x^2 } } ];
y = Map[ makeLine, x ];
Show[ Graphics[ y ] ];
If you like one-liners, this also works:
Show[ Graphics[ Line[ { { 5, 25 }, { #, #^2 } } ]& /@ x ] ]
Here I have used the & operator to make an inline function
declaration and have used the /@ abbreviation for the Map
function.
Good luck and keep trying.